Method of vulcanizing rubber and product thereof



Patented Jan. 15, 1952 MET-Hon F VULCANI'ZING RUBBER AND O UCT HEBEQERichard 0.'-Zerbe,- Nitro, W. Va., assignor to Monsanto ChemicalGompany, St. Louis, Mo., a corporatiomof Delaware No Drawing.Application January 17, 1949,

7 Serial N0. 71,409,

16 Claims. (o1. 260-795) This invention relates m. the. Ma atee-i1 Br: 1

rubber. More particularly it relates thef'vul n' z b o ubber i h a eclass accent-1 1 tors} andvv to the, vulcanized products; resulting 3thereby;-

Inthe compounding of rubber, both natural and synthetic, improvementshave'beenconstantly sought, particularlyin respect to the more ef ficentand more economical use of vulcanization accelerators. While manyaccelerators, perse, produce vulcanizates having acceptable physicalproperties, it has long been known' 'thatby the incorporation into thecompoundedstock of accelerators such as dibutyl ammonium pleate" anddiphenyl guanidine-phtha'late in addition to other type accelerators;such. as th'e-thiazoles, greater ease in processing and a better"Vulcanizate is obtained; It has become customary to denote' materialssuch as dibutyl' olea'te a d diphenyl e i n phtha te and the like asactivators. Similarly it is preferred tov p y the new etatc siconjunction with accelerators of other, types s aetivatgm :It is anobject fithis-inventiomm provide; a. class of activators which arecapableofiassisting accelerators possessing inherent weaknesses, such asinefllcient vulcanizing effect, limited solubility, and poordispersibility in rubber stocks, thus causing uneven cures which in turnresult, in non-uniform properties and erratic performance in service. Itis also an object of this invention to decrease the time ofvulcanization. 1 A further object isv to provide a wider choice ofcuring conditions such that a series of combinations varying in scorchand curing properties may be obtained. For example, the ratio ofactivator to accelerator may vary dependingjupon thetype of rubber/typeof stock-temperature of cure, time of cure, the particular accelerator,and the objective of the compounder, i. e., whether a low halfamidesbrjaicarbdsyne ac ds as t eir salts ot the following general formula n,where M is hydrogen or a salt forming group such as a metal, ammonia-anamine, urea,'and the like; where R1 and Rz are alkyl, cycloalkyl, andaralkyl groups such as methyl, ethyl, ethanol.

.;propyl, butyl, amyl, cyclohexyl, methyl cycloor high modulus isdesired or a short or long cure is required. Other objects will appearhere- 1 inafter.

vention that the above mentioned objects are at f tained by vulcanizinga vulcanizable rubber stock in which has been incorporated a. member ofthe a group of compounds comprising amic acids, or

hexyl, benzyl, phenethyl, and their various qqmerie roup's, ca bam l andy roc b n su un e mvl adical hio a b mvl and hvdrocarbonsubstituted'thiocarbamyl radicals, and the like/and whereeither orbothR1 or R; anay be hydrogen; whereR is an ethylene or propylene group orsubstituted homologue or "analogue thereof. Among the salt formi-nggroups are the alkali, and, alkaline earth metals, zinc, magnesie and tk mmon ethyl amin ethylaminegethanol amine fg-oyanoethyl amine, iso.-.propyl amine, amyl; amine, butyl amine, zr-cyanoe butyl amine,cycloh'eizyla'rr'line, benz'yl amine, diethyl amine, diethanol amine,di-(Z-cyanoethyl) m ne. Qi-i QQ 'QPYl amine. d bu l mine. m t

v pr py am n cyclo exy ami e, iben yl.

m e. amend-me. im yl am ne meth mine. and the ike .Alt weeem c a i s andhe r sa t of t e above described general formula produce good. su s ee-bst r su t a e ta ne t se imm e ac d, itsmet a s a d, i lky ancycloalkyl-Vamine-salts, wherein at least one hydrogen atom of the amidonitrogen is replaced by an alkyl or cycloalkyl group. As specific expfiS. 9f Illgi' are s i m @Q isopropyl succinamic acid, N-butylsuccinamic acid, N-cyclohexyl succinamic acid, N,N-dicyclo.- hexylsuccinamic acid, ethyl amine salt of N- ethyl succinamic acid, butylamine salt of N- butyl succinamic acid, di-isopropylaminesalt ofN;N-di-isopropyl succinamic acid, dicyclohexyl' amine salt ofN,N-dicyc1ohexyl' succinamic, acid,

.zinc salt of N-butyl succinamic acid, zinc salt of Example 1 40 partsby weight (substantially 0.4 mols) of succinimide was added to 200 cc.of water in a suitable reaction vessel and immersed in a steam bath. Tothe aqueous solution was added 62 The above stocks so compounded werevulcanized in the usual manner by heating in a press for difierentperiods of time at 142 C. The physical properties of the respectivecured rubber stocks are set forth below:

Table I Min. Stock Cureat A B O D E F 142 o.

60 e0 80 160 so no cure 300% modulus, 1bs. in.=-- 125 170 175 178 150Do. l v U 4o no 163 165 167 141 Do. 1 1o isa 283 433 750 625 Do.500%modulus,lbs./in. 20 623 820 788 878 870 Do.

. 40 e40 135 708 800 780 260. r 10 820 1.268 1,490 2,958 2,230 nocure100% modulus, lbs/in!" 20 2,168 3,055 2.718 3,220 2,903 Do. i8 @322 i838Ultimate tensile I 20 2,255 4,100 6,135 4,125 3,255 Do. F 2. F: P"----?-40- am. 3,940 2,888 4,103 3,340 1.810.

I 10 758 840 793 795 738 no cure Ultimate elongation, 20 718 778 755 773753 Do. I 40 780 785 140 770 753 810.

parts by weight (substantially 0.2 mols) of barium hydroxide octahydrateand the white salt of barium succinamate filtered off. The salt was thendissolved in sulfuric acidand the barium sulfate salt filtered off. Thefiltrate was evaporated to dryness, the residue taken up with acetoneand the impurities filtered off. Upon removal of the solvent, 25.2 partsby weight of a white powder, believed to be succinamic acid, wasobtained having a melting point of 156-157 C.

Example 2 dark purplish-gray-black solid believed, to bethe dicyclohexylamine salt of N,N-dicyclohexyl nielting point range of 117- 125 e 7Example 3 7 succinamic acid developed which possessed a parts by weight(substantially025 mols) ot succinic anhydride was placed in a suitablecontainer and thereto at a temperature below 25 C. was added 36.6 partsby weight (substantially 0.5 mols) of butyl amine, over a period of 20minutes with constant agitation. Upon completion of the amine additionthe temperature was al-[ lowed to rise and a clear yellow liquiddeveloped. Upon cooling 61.5 parts by weight of a' clear yellow liquid,believed to be the butyl amine salt of N -butyl succinamic acid, wasisolated.

As exemplary of the activating properties of the amic acids, thefollowing gum stocks were compounded:

Zinc oxide 55 Sulfur It is obvious from the above data the amic acids ina short time. "The new activators are readily "compatible in rubberstocks, both natural'and synthetic, and are non toxic; The amic acidsalso exhibit a marked activating efiect on the cure rate of syntheticrubber such as GR-S.

As exemplary of the activatable organic accelerators or primaryaccelerators are the mercapto Smaller amounts or the amic acidactivators may be employed than those'indicated in the specificexamples. It has been found that as little as 0.2% on the rubber of amicacid is efiective. Amounts higher than those specifically shown, as forexample 2%, can be employed depending jectives of the compounder.

"Theamic acids andtheir salts of themselves possess vulcanizationaccelerator properties. Forexample" the following naturalgum rubberstocks were compounded comprising Stock- Smoked shects'runber... v.QLQQparts by weight" 1 Stear'ic acid Butylamiuo salt of N- tyl s-..do..

Dicyclohexyl amine salt of N ,N-dicyclo-hexyl succinamic acicL; parts byweight..

'The above stocks so compounded were vulcan ized in the usual manner byheating in a press for and minutes respectively at 142 C.

Stock A, B 0 v D E r r Smoked sheetsrubber pa|ts by weight- 100 100 100100 100 ZlIlC oxide do 35 35 35 35 35 35 111 i' d0 1. 3 1.3 1.3- 1.3 V,1.3 1.3 Stearic acid do 1. 0 l. 0 l. 0 1.0 31. 0 1. 0 Benzothiazyldisulfidm. d0--- 0. 6 0.6 I 0.6 v 0.6 0.6 0.6 succinamic acid do 1. 0 VDicyclohexylamine salt of N,N

dicyc lohexyl succinamic 301d parts by-welght. 1.0 0.5 i Bptyl aminesaltf N-butyl. f; i

succmamic acid-- .parts by weight. 1.0. 0. 5

thiazoles, the mercapto-arylene thiazoles, the

upon the conditions of compounding and the ob- The following bbtainedaentesting the curedrubber products:

By the term rubber as employed in the appended claims is meant naturalas well as synthetic rubbers which are capable of vulcanization whenheated with sulfur and includes latices and reclaims of such materialswhether or not admixed with pigments, fillers, softeners, antioxidants,etc.

While specific embodiments of the invention have been described herein,it will be understood that the invention is not so limited but thatvarious modifications may be made therein without departing from thespirit of the invention or from the scope of the appended claims.

What is claimed is:

1. The method of vulcanizing a rubber which comprises heating a rubberand sulfur in the presence of a small amount of a compound selected fromthe group consisting of acids of the structure 0. 0H R-C O.NRi

and salts thereof where R is an alkylene group containing more than onebut less than four carbon atoms and where R1 and R2 are selected fromthe group consisting of hydrogen, alkyl radicals of one to five carbonatoms inclusive and their monohydroxy and monocyano substitutedderivatives, benzyl, phenethyl, cyclohexyl and methylcyclohexylradicals.

2. The method of vulcanizing rubber which comprises heating rubber andsulfur in the presence of 0.2% to 2% based on the weight of the rubberof a succinamic acid wherein at least one hydrogen atom of the amidonitrogen is replaced by an aliphatic hydrocarbon radical containin oneto seven carbon atoms inclusive.

3. The method of vulcanizing rubber which comprises heating rubber andsulfur in thepresence of 0.2% to 2%- based on the weight of the rubberof an amine salt of a succinamic acid wherein at least one hydrogen atomof the amido nitrogen is replaced by an aliphatic hydrocarbon radicalcontaining one to seven carbon atoms inclusive.

4. The method of vulcanizing rubber which comprises heating rubber andsulfur in the presence of a thiazole accelerator and 0.2% to 2% based onthe weight of the rubber of a succinamic acid wherein at least onehydrogen atom of the amido nitrogen is replaced by an aliphatichydrocarbon radical containing one to seven carbon atoms inclusive.

5. The method of vulcanizing rubber which comprises heating rubber andsulfur in the presence of a thiazole accelerator and 0.2% to 2% based onthe weight of the rubber of an amine salt of a succinamic acid whereinat least one hydrogen atom :of theiamidopnitrngeni-is replaced by analiphatic hydrocarbon mad-icallcontainingi one xto seven-s carbon :atomsinclusive.

rubber of the butyl'amine salt of N-butyl succinamic acid.

7. The method of wulcanizing rubber which om ri hea n s b erand u -sta nth me ence of 0.2% to 2% based uponfthe-weightpf the rubber of thedicyclohexyl amine salt of N,N- dicyclohexyl succinamic acid.

8. The method of vulcanizing rubber which comprises heating rubber andsulfur in the presence of 0.2% to 2% based upon the weight of the rubberof succinamic acid and a thiazole accelerator.

9. The vulcanized rubber product obtained by heating a rubber and sulfurin the presence of a small amount of a compound selected from the groupconsisting of acids of the structure and salts thereof where R is analkylene group containing more than one but less than four carbon atomsand where R1 and R2 are selected from the group consisting of hydrogen,alkyl radicals of one to five carbon atoms inclusive and theirmonohydroxy and monocyano substituted derivatives, benzyl, phenethyl,cyclohexyl and methylcyclohexyl radicals.

10. The vulcanized rubber product obtained by heating rubber and sulfurin the presence of 0.2 to 2% based on the weight of the rubber of asuccinamic acid wherein at least one hydrogen atom of the amide nitrogenis replaced by an aliphatic hydrocarbon radical containing one to sevencarbon atoms inclusive.

11. The vulcanized rubber product obtained by heating rubber and sulfurin the presence of 0.2% to 2% based on the weight of the rubber of anamine salt of a succinamic acid wherein at least one hydrogen atom ofthe amido nitrogen is replaced by an aliphatic hydrocarbon radicalcontaining one to seven carbon atoms inclusive.

12. The vulcanized rubber product obtained by heating rubber and sulfurin the presence of a thiazole accelerator and 0.2% to 2% based on theweight of the rubber of a succinamic acid wherein at least one hydrogenatom of the amido nitrogen is replaced by an aliphatic hydrocarbonradical--containing one to seven carbon atoms inclusive.

13. The vulcanized rubber product obtained by heating rubber and sulfurin the presence of a thiazole accelerator and 0.2% to 2% based on theweight of the rubber of an amine salt of a, succinamic acid wherein atleast one hydrogen atom of the amido nitrogen is replaced by analiphatic hydrocarbon radical containing one to seven carbon atomsinclusive.

14. The vulcanized rubber product obtained by heating rubber and sulfurin the presence of 0.2% to 2% based upon the weight of the rubber of thebutyl amine salt of N-butyl succinamic acid. a

15. The vulcanized rubber product obtained by heating rubber and sulfurin the presence of 0.2% to 2% based upon the weight of the rub! 26895789. 7; her of the dicyclohexyl amineglt oi N,N-'dicyc10 -i L :7 1UNITED STATES PATENT-S hexytsuccinamic acid.'::-.-i'.. 7 (=57 V; H 7 7 r16. The vulcanized rubber product obtained "by; g??? Aug i heatingrubber-11nd;sulfur Kin 'the'presence of 201311T nTuley Sep't 1935 to 2%based upon the weight .of themm-v 5 2034889 g 1936- ber-of succinamicacidand a thiazo1e accelerator; 2131127 Horst, Tu-- t, 27 93 RICHARDOLZERBELi 'T' v ,v FOREIGN PATENTS REFERENCES Number Country Date Thefollowing references are 01 fedora-in the 10 394,754 Great "B;r 1tg11; J11y 6, 1933 file LthIsPaltenJtF a

1. THE METHOD OF VULCANIZING A RUBBER WHICH COMPRISES HEATING A RUBBERAND SULFUR IN THE PRESENCE OF A SMALL AMOUNT OF A COMPOUND SELECTED FROMTHE GROUP CONSISTING OF ACIDS OF THE STRUCTURE